Tests to reveal where Canada's single BSE-infected cow picked up the disease have proved inconclusive, meaning officials will have to slaughter and test around 650 more cattle to be sure that no others are infected with the disease. The genetic tests compared the DNA of the infected cow with that of bulls on farms at which the cow had been kept during its lifetime. Despite its exact origin remaining unclear, investigators still believe the cow came from one of a series of farms in Saskatchewan and Alberta, according to chief veterinarian Brian Evans.